Bone is living tissue. As we age, new bone is created more slowly than old bone is removed. When we're past 35, we lose, on average, about 1 percent of our bone mass each year.

If our bones become so weak and brittle that minor stress can cause a fracture, the condition is called osteoporosis (porous bones). About 50 percent of women and 25 percent of men over 50 will break a bone due to osteoporosis, according to the National Osteoporosis Foundation.

Women are much more likely than men to develop osteoporosis because they have less bone mass to lose to start with, they live longer and bone mass loss tends to accelerate after menopause.

The risk of osteoporosis and osteopenia (bone mineral density is low but not yet dangerously low) can be reduced through diet and exercise. If we walk a mile or more a day, we can add about 1 percent a year to bone mass, research at Tufts University indicates. That's enough to offset bone loss from aging.

We can increase bone density if we wear a weighted vest when we take our walks or when we work out, says Victor Prisk, an orthopedic surgeon for the West Penn Allegheny Health Care system.

"Bone responds to stress," said Dr. Prisk, who in his spare time is a champion body builder. "If you add more weight to your skeleton, you'll grow more bone faster."

Dr. Prisk was a gymnast in high school and college. He began wearing a weighted vest while he was doing resistance exercises, such as push-ups and pull-ups, to build strength faster. A study of athletes at Texas Tech University indicated athletes who wore a weighted vest during traditional resistance exercises had "substantially" better results after six weeks than athletes who didn't.

If you wear a weighted vest while exercising, you'll burn more calories, so it may also accelerate fat loss. People who wore an 8-pound vest while exercising burned 23 percent more calories than people who didn't, according to a study by Prevention magazine.

Dr. Prisk's wife, Kristini Curci, a psychiatrist at UPMC Mercy, who is also a body builder, wears a weighted vest sometimes when she works out on the treadmill or the elliptical machine they have at home.

"I used to do it mostly to increase the intensity of the workout, but now I do it mostly to prevent bone loss," Dr. Curci said. "With women you've got to watch that spine."

Several small studies of post-menopausal women who wore weighted vests while doing exercises such as jumping or climbing stairs increased bone density.

Some of the same benefits can be obtained by carrying weights in your hands when you walk, jog, or climb stairs. But, said Dr. Prisk, "one of the nice things about a vest is it hugs your body. It's much safer than weights in your hands or ankles in that it keeps it close to your body."

Although they're safer, there are some risks with vests if they fit poorly or you use too much weight. For beginners, a vest that adds about 3 percent of body weight is recommended. It shouldn't ever weigh more than 15 percent of body weight.